A method of applying a hose section to a cable

Abstract

 In a method of applying a tight-fitting hose section (3) to a cable (2), where the hose section is expanded radially while being slid in over the cable, one end of the hose section is forced in over the cable end and is given an increased resilient engagement force with respect to its ordinary engagement force against the cable, e.g. by a bend (4), and then the hose section is expanded radially by means of fluid pressure (5-9). When the hose section is then moved in over the cable, the cable displaces fluid which excapes at (10), where a fluid cushion is provided, so that there is practically no friction between the hose section and the cable. When the hose section is in place, the fluid pressure is relieved and the fluid pocket between the cable and the hose section is expelled.

Description

[0001] The invention concerns a method of applying a tight-fitting, elastic hose section to a cable, the hose section being expanded radially during its movement over the cable.

[0002] It will be appreciated that the expanded part of the hose section does not give rise to frictional force against the cable, as explained e.g. in the German Offenlegungs- schrift 26 21 641. This prior art concerns a relatively rigid sleeve in particular, whose frictional force is reduced because of the radial expansion, but on the other hand sealing means are provided at the ends of the sleeve which cause increased frictional resistance against the cable in order for the pressurized air to be kept within the sleeve.

[0003] The US Patent Specification 3 138 859 discloses a technique, which concerns application of a hose or tube section and is of the type where the hose section is expanded radially during its movement over the cable by forcing one end of the hose section in over the free end of the cable, and by closing the other end of the hose section, and then subjecting the hose section to fluid pressure. The latter art, which does not comprise sealing between the hose section and the cable does not lend itself to long hose sections, because relatively strong flow is required to reduce the friction sufficiently. This causes a large pressure drop and correspondingly large counter-pressure which renders the assembly difficult, as well as a risk of irregular radial expansion of the hose section. The latter drawbacks are remidied according to the said specification by means of an external support tube, but the large counter-pressure and fluid consumption as well as the presence of the support tube are a serious disadvantage in practice.

[0004] The object of the invention is to provide a method of applying a hose section over a cable end, which practically eliminates friction between the hose section and the cable, and minimizes the fluid consumption and counter-pressure.

[0005] This object is achieved by giving said one end of the hose section an increased elastic engagement force with respect to its ordinary engagement force against the cable prior to subjecting the hose section to fluid pressure, so that the prevailing fluid pressure is dependent upon the said increased engagement force at one end of the hose section. The increased engagement force at one end of the hose section partly involves a well-defined positive pressure in the hose, which can thus be expanded to a cross section greater than that of the cable, and partly permits the enclosed fluid to excape at the said end of the hose section as the fluid is displaced from the cavity of the hose section by the cable. When the fluid escapes at said hose section end, it will ride on a fluid cushion so that there is practically no friction between the cable and the part of the hose section which has been given an increased resilient engagement force. It will be appreciated that this method also results in minimum counter-pressure and fluid consumption.

[0006] The resilient engagement force can e.g. be increased by application of a rubber band around one end of the hose section, but preferably the engagement force is increased by bending the outermost part of one end of the hose section backwardly over the hose section, thus obviating additional components. When the hose section has been slid in over the cable, the backwardly bent part is straightened so that a substantial part of the fluid excapes. In some cases, however, it is impossible to avoid the occurrence of fluid pockets between the hose section and the cable. Such pockets may cause undesirable electric discharges in high-voltage cables, but may be removed by relieving the fluid pressure by rolling an elastic ring across the hose section, the elastic engagement force of the ring against the cable being greater than the said increased engagement force. Such a ring or optionally several rings can moreover be utilized for clamping the ends of the hose section harder against the cable, e.g. to prevent ingress of water, and the use of a ring, which has a circular cross-section and consists wholly or partly of a semi-conductive material, provides the additional advantage in high-voltage cables that the semi-conductive ring, when given the same potential as the conductor of the cable, e.g. by a metallic connection between the ring and a cable lug, prevents concentration of the electric field around sharp edges on the electrically conductive parts when the ring is applied closely adjacent to the sharp edges.

[0007] Preferably, the hose section is made of silicon rubber, and the fluid is usually air. In a preferred embodiment the other end of the cable is closed by means of a plug having a through bore which communicates with a rubber ball provided with check valves, so that just a very simple and reliable aid is required in the mounting of the hose section.

[0008] The invention will be explained more fully by the following description of a preferred embodiment with reference to the drawing, in which

[0009] figs. 1-4 show various stages in the application of the hose section in accordance with the method of the invention.

[0010] Fig. 1 shows a free end of a cable comprising an electric conductor 1 and an associated insulation 2. The figure moreover shows an elastic hose section 3, which is to be slid in over the cable by the method of the invention. The hose section 3 is shown in a position in which its one end is pulled in over the insulation 2 and bent backwardly at 4, while the other end of the hose section has mounted therein a plug 5 with a through tube 6 connected to a rubber ball 7 which contains check valves 8, 9. The latter parts are commercially available.

[0011] As shown in fig. 1 the cross sectional dimension of the hose section in an unexpanded state is smaller than the cross sectional dimension of the cable so that the mounted hose section will be a tight fit around the cable. Pressurized air is then introduced into the hose section by means of the rubber ball 7, causing said hose section to expand to a cross sectional dimension which is larger than the cross sectional dimension of the cable (when the conductor consists of several twisted threads, a sealing substance may be applied to the end to avoid ingress of air into the conductor). The backwardly bent part 4, however, brings about an increased engagement pressure against the cable, so that the air can escape through the backwardly bent part and the cable when the air pressure is sufficiently great in the hose section. When this is the case, it is not necessary to introduce more air into the hose section since this can readily be moved in over the cable as shown in fig. 2.

[0012] Fig. 2 shows the hose section as slid partly in over the cable, some spacing between the cable and the internal wall of the hose section being clearly visible, so that no frictional force prevails at this location. When the hose section is moved in over the cable it should be noted however that the cable displaces the cavity in the hose section so that pressure increases in the hose section. The expanded part of the hose section, however, will substantially maintain its cross sectional dimension because the excess of air excapes between the backwardly bent part 4 and the cable, which is indicated by a gap 10. Thus, the gap 10 causes the backwardly bent part of the hose section to ride on an air cushion when the hose section is moved in over the cable, so that there is practically no friction between the hose section and the cable.

[0013] In fig. 3 the hose section has been moved into position over the cable, and the rubber ball and the plug have been removed. Excess hose section can be cut off and/or bent backwardly as shown at 11 in fig. 3. This enables stripping of the cable and e.g. mounting of a cable lug 12 on the electric conductor. To enable a tight fit between the hose section and the surface of the cable it is necessary to expel air pockets, if any, between the hose section and the cable. This is done according to the invention by means of a ring 13, e.g: a strong 0-ring, which is manually rolled down over the hose section placed on the cable. The resilient engagement force of the ring against the hose section is of course to overcome the pressure in the air pockets, so it will be appreciated that this results in effective venting of the.pockets. Mcreover, one or more such rings may be left on the hose section to prevent any ingress of water between this section and the cable.

[0014] It will be seen in fig. 4 that the backwardly bent part 11 has been straightened and extends across the cable lug 12. However, it is observed that there is a small gap 15 between the insulation of the cable and the cable lug, which is normally necessary for the use of the tools used for clamping the cable lug. The positioning of a ring 14 adjacent this gap provides a more effective seal because the ring presses against the edges of the insulation and the cable lug, and the use of a ring consisting wholly or partly of a semi-conductive material in accordance with the invention provides the advantage that no concentrations of the electric field occur at the edge of the cable lug. This presupposes however that the ring 14 has the same potential as the conductor 1, which can e.g. be achieved by means of the electrically conductive strip 16 shown in fig. 4.

[0015] It will thus be appreciated that the method of the invention allows insertion of practically any length of hose over the cable without noticeable friction. This can be obtained no matter whether the cable cross section is round, sector-shaped or of any other shape, and it is moreover possible to use a single hose type in connection with various cable thicknesses within a relatively large region. Finally, it is observed that the method is also relevant in connection with splicing of cables as the hose section can very easily be positioned over one cable end. When two cable ends have been spliced together, both ends of the hose section may be bent backwardly and pressurized air may be introduced between the cable insulation and one end of the hose, following which the hose section can be slid in over the splice.

Claims

1. A method of applying a tight-fitting elastic hose section to a cable, wherein the hose section is expanded radially during its movement over the cable by forcing one end of the hose section in over the free end of the cable, and by closing the other end of the hose section, and then subjecting the hose section to fluid pressure, characterized by giving said one end of the hose section an increased elastic engagement force with respect to its ordinary engagement force against the cable prior to subjecting the hose section to fluid pressure, so that the prevailing fluid pressure is dependent upon the said increased engagement force at one end of the hose section.

2. A method according to claim 1, characterized by increasing the engagement force by bending the outermost part of one end of the hose section backwardly over the hose section.

3. A method according to claim 1 or 2, characterized by relieving the fluid pressure by rolling an elastic ring across the hose section, the elastic engagement force of the ring against the cable being greater than the said increased engagement force.

4. A ring for performing the method of claim 3, characterized in that the ring has a circular cross section, and that it consists wholly or partly of a semi-conductive material.

Drawing